A commonly used prior art mechanism for picking and feeding of media sheets employs a D-shaped wheel which is rotated to cause a media sheet pick action. During a sheet feed subsequent to a pick action, the flat section of the D-wheel remains out-of-contact with the fed sheet. This arrangement is satisfactory so long as the media sheet, during a feed operation, is not bent around the D-wheel shaft. This may occur when the media tray is positioned at an angle to the feed mechanism. Under such a circumstance, the media sheet must bend as it is fed into the print mechanism. If the media sheet presses against the D-shaped wheel, significant drag on the media sheet results. A solution to this problem has been to affix a pair of free-wheeling disks to the same shaft on which the D-wheel is mounted. These disks protrude beyond the flat section of the D-wheel (or wheels) thereby enabling the media sheet to be pressed against the disks instead of the D-wheel during the feed operation. A further solution to this problem is the use of an additional shaft after the D-wheel shaft so that the media sheet bends around circular rollers on the additional shaft. Both solutions add to the part count and cost of the media sheet pick and feed system.
Another prior art pick and feed system is shown in FIGS. 1-3 which illustrate a pick roller system employed in a media sheet feed mechanism manufactured by the Epson Corporation. FIG. 1 is a side view of the Epson pick wheel and comprises a drive gear 10 that is mounted on a shaft 12 which is, in turn, coupled to a drive motor (not shown). A pivot arm 14 is mounted for rotation about shaft 12 and encloses a rubber pick roller 16. A driven gear 18 mates with drive gear 10, is rigidly connected to rubber pick roller 16, and is mounted for rotation on a shaft 20. A spring washer 22 is positioned between an inner surface of arm 14 and driven gear 18 and performs a friction clutch function.
A media tray includes a pressure plate 24 which supports a stack of media sheets 26 and is biased by a spring 28 into contact with rubber pick roller 16. An edge separator 30 is positioned to maintain an uppermost sheet on stack 26 in place until operation of rubber pick roller 16.
Referring to FIGS. 2 and 3, schematic views are shown of the pick roller and feed system of FIG. 1. To implement a pick operation, drive gear 10 is driven in a counter clockwise (CCW) direction thereby causing driven gear 18 to rotate in a clockwise (CW) direction. Due to the friction exerted by spring washer 22, arm 14 and pick roller 16 are caused to rotate in a CCW direction until arm 14 hits a stop 32. This action causes pick roller 16 to come into contact with an uppermost sheet of stack 26, which uppermost sheet is, in turn, forced against pick roller 16 through the action of spring 28 on tray 24. Continued clockwise rotation of pick roller 16 causes a feed of an uppermost sheet 34 from stack 26.
As shown in FIG. 3, when uppermost media sheet 34 is grabbed by a pair of feed rollers 36, the direction of rotation of driven gear 10 is reversed to a CW direction, thereby causing arm 14 and pick roller 16 to rotate in a CCW direction and out of engagement with uppermost sheet 34. The CCW rotation of pick roller 16 is required as the clutching action of spring washer 22 would cause pick roller 16 to impede the feeding of media sheet 34, were it not brought out of engagement. The CCW rotation of arm 14 and pick roller 16 continues until arm 14 hits a second stop 38.
The use of a spring loaded tray may require that the media sheet tray be removed for media sheet reloading or that a camming mechanism be provided that depresses the pressure plate to enable reloading. The camming mechanism increases torque requirements on the mechanism drive motor.
Accordingly, it is an object of this invention to provide a media sheet pick and feed system which exhibits decreased torque drive requirements and can be easily reloaded with media sheets.
It is another object of this invention to provide an improved media sheet pick and feed system wherein the position of the pick roller automatically adjusts to height variations of a stack of media sheets.
It is yet another object of this invention to provide an improved media sheet pick and feed system which employs a fixed position media sheet tray and requires no spring loading of media sheets against a pick roller.
It is yet another object of this invention to provide an improved media sheet pick and feed system that is capable of a handling a wide range of paper weights.